1. Field of the Invention
The present invention relates to electronic devices having navigation functions for searching for routes to a destination and displaying a map around a current vehicle position, and in particular, relates to methods for displaying night-view maps.
2. Description of the Related Art
A navigation apparatus detects a current vehicle position, reads out data of a map around the current vehicle position from a map database, draws a map on a display, and superimposes a vehicle mark on the map. When the current vehicle position changes in response to movement of the vehicle, the map scrolls and the vehicle mark moves in response to the movement of the vehicle.
A map to be displayed preferably shows images of, for example, actual roads and intersections, as closely as possible and presents the images to users as guidance information in a plain format. Particularly, in displaying, for example, intersections and towns at a large scale, the map is preferably designed with, for example, a three-dimensional display technique so that users can perceive reality.
At a scale used for displaying a relatively wide area, a map is often flat and feature-less. As disclosed in Japanese Unexamined Patent Application Publication No. 2000-283784, when a scale of 1 to 160,000 or more is used for displaying a wide area, a map is displayed using picture data that is shot from a satellite and stored in advance.
When the scale of a map is small, an area to be displayed is expanded to include a large number of buildings and the like. However, the number of pixels (resolution) in the horizontal and vertical directions on a display, such as a liquid crystal display, is limited. When all buildings and the like are displayed in this situation, they are so close to each other that users cannot clearly recognize them. Thus, no buildings and the like are displayed at a small scale below a predetermined level.
When no buildings and the like are displayed at a small scale, the screen is feature-less, so that users cannot perceive the actual situation and cannot find the screen appealing. When no buildings and the like are displayed in a nighttime display mode that is switched on in response to time or a vehicle light (light switch) being turned on, a large part of the screen may appear black. On the other hand, when picture data is used at a small scale, as disclosed in the foregoing document, high costs are involved in creating, processing, and storing the picture data.